The ability of the morphological right ventricle (RV) to support the systemic circulation is limited. It has been postulated that perfusion and wall motion abnormalities are common in the systemic RV late (10-20 years) after Mustard's operation. Poor ventricular function causes progressive RV enlargement and systemic atrioventricular valve insufficiency, resulting in congestive heart failure (CHF). Deterioration in systolic function of the systemic ventricle is a major determinant of survival in these patients.